Mikihito Takenaka

Fabrication of Two‐Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox‐Active Coordination Nanoslits

1 / 1 Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University Title: Fabrication of Two-Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox-Active Coordination Nanoslits Author: N. Yanai, T. Uemura, M. Ohba, Y. Kadowaki, M. Maesato, M. Takenaka, S. Nishitsuji, H. Hasegawa, and S. Kitagawa Journal: Angew. Chem. Int. Ed., Vol. 47, No. 51, 9883-9886 (2008) Abstract: Oxidative and intercalative polymerization of pyrrole was conducted within the nanoslits of a layered coordination open framework containing redox-active sites. Isolation of polypyrrole from the host framework led to stacked sheet polymer objects whose orientation and morphology are directly related to the original coordination polymer template.

Spontaneous pinning of domain growth during spinodal decomposition of off‐critical polymer mixtures

Spinodal decomposition of off‐critical mixtures of poly(styrene–random–butadiene) copolymer with polyisoprene or polybutadiene was investigated as a function of the composition w of the mixtures and of the phase separation temperature T by time‐resolved light scattering. The coarsening behavior of the mixtures was characterized in terms of the time change of the maximum intensity Im and that of the magnitude of the scattering vector qm at which the intensity becomes maximum. It was found that the time changes of Im and qm for the off‐critical mixtures studied here are effectively pinned at a certain time defined here as the ‘‘pinning’’ time. This spontaneous pinning of the growth of the unmixing structure was found to occur earlier when w is biased toward 0 or 1 at a given T and when the phase separation temperature is raised at a given w, for these systems which seemingly have upper critical solution temperature behavior.

Scattering studies of self-assembling processes of polymer blends in spinodal decomposition. II: Temperature dependence

Our previous work on time evolution of the interfacial structure for a near critical mixture of polybutadiene and polyisoprene undergoing the spinodal decomposition (SD) [T. Hashimoto, M. Takenaka, and H. Jinnai, J. Appl. Crystallogr. 24, 457 (1991)] was extended to explore the behavior as a function of temperature T, again using the time‐resolved light scattering method. The study involved the investigation of the time evolutions of various characteristic parameters such as the wave number qm(t;T ) of the dominant mode of the concentration fluctuations, the maximum scattered intensity Im(t;T ), the scaled structure factor F(x;T ), the interfacial area density Σ(t;T ), and the characteristic interfacial thickness tI(t;T ) from the early‐to‐late stage SD, where t refers to time after the onset of SD and x refers to the reduced scattering vector defined by x=q/qm(t;T ); q is the magnitude of the scattering vector. The results confirm the model previously proposed at a given T over a wider temperature range ...

Scattering studies of self‐assembling processes of polymer blends in spinodal decomposition

Structure self-assembling in the spinodal decomposition (SD) of polymer blends in its late stage has been explored for a near-critical mixture of polybutadiene and polyisoprene by a time-resolved light scattering technique, with a particular emphasis on the time evolution of the interface structure. By analysis of a scaled structure factor F(x, t)I(q, t)qm(t) 3 over wide ranges of a reduced scattering vector x - q/qm(t) and time, it was found relevant to divide the late stage of SD into two stages, I and II. Here, I(q, t) denotes the scattered intensity as a function of the scattering vector q and time t. In the intermediate stage preceding the late one, F(x, t) became sharper with its peak at x = 1 increasing with t. However, as time elapsed, F(x, t) turned out to be universal for t, first in the range of x smaller than about 2 and then over the entire range of x accessible by the present experiment. The time interval in which the former occurred is defined as late stage I and the one in which the latter was realized is called late stage II. In late stage I, the average thickness of phase-phase interfaces decreases towards an equilibrium value and the time evolution of the interfacial area density .,Y(t) does not scale with q,,(t), i.e. the exponents y and a in the power laws 2:(0 - t-~ and qm(t) N t-~ do not coincide (actually, a < y). Late stage II corresponds to the process in which these exponents become equal and the interface thickness reaches equilibrium. Such conditions probably ensure the establishment of a complete dynamical scaling law in the SD process.

Slow spinodal decomposition in binary liquid mixtures of polymers. IV. Scaled structure factor for later stage unmixing

The later‐stage spinodal decomposition (SD) of polymer mixtures at deep quenches were investigated by time‐resolved light scattering. The scaled structure factor F(x)≡qm (t,T)3I(x) with x≡q/qm (t,T) was analyzed as a function of time t or reduced time τ during the SD at various temperatures T’s, where qm (t,T) is the magnitude of the scattering vector q at which the first‐order peak of the scattering intensity profile I(q;t,T) appears. Spectacular features in F(x) were discovered; (i) F(x) at large x is not universal with t but rather increasing with t, implying that the local structure is not scaled with a single length parameter 1/qm (t,T) used for the scaling of the global structure at x≂1, (ii) F(x) shows the second‐ and the third‐order peaks or shoulders at x=2 and 3, and (iii) F(x) exhibits a dynamical crossover from x−n (n≂6) to x−4 with t in the asymptotic behavior at x≳2, as well as a spatial crossover from x−n to x−4 with x at τ in the sufficiently late stage.

Spontaneous pinning of domain growth during spinodal decomposition of off‐critical polymer mixtures. II. Scaling analysis

Later‐stage spinoidal decomposition (SD) of off‐critical mixtures of poly(styrene‐ran‐butadiene) SBR/polyisoprene or SBR/polybutadiene was investigated by time‐resolved light scattering. Changes in the scaled structure factor F(x,t)≡qm(t)3I(x,t) with x≡q/qm(t) were determined as a function of the composition w of the mixture and of the phase separation temperature T, where qm(t) is the wave number q at the peak position of the scattering intensity profile I(q,t) at time t. It was found that the later‐stage SD for the off‐critical mixture is divided into four stages: intermediate, pseudolate, transition, and pinning. The change in the structure factor F(x,t) at large x implied that the dynamical percolation‐to‐cluster transition occurs before the pinning stage.

Experimental studies of stress-diffusion coupling in semi-dilute polymer solutions. I. 'Viscoelastic length' and viscoelastic effects on early stage spinodal decomposition

Abstract We investigated the viscoelastic effects on the early stage spinodal decomposition (SD) in semi-dilute polymer solutions where the coupling between stress and diffusion plays an important role. The so-called viscoelastic length, ξ ve , within which the stress suppresses the growth of the concentration fluctuations, was quantitatively evaluated experimentally. The evaluated value was found out to be about 10 times larger than the radius of gyration of polymer. We measured the interdiffusion coefficient, the cooperative diffusion coefficient, the zero-shear viscosity, and the plateau modulus in the one phase region and evaluated ξ ve independently from the SD experiment. The value ξ ve obtained in the early stage SD agrees well with that estimated from the diffusion and viscoelasticity measurements, confirming the validity of the Doi–Onuki theory.

Arm-Cleavable Microgel Star Polymers: A Versatile Strategy for Direct Core Analysis and Functionalization

Arm-cleavable microgel star polymers were developed, where the arm chains can readily be cleaved by acidolysis after the synthesis, allowing isolation of the core, direct analysis of its structure, and also the creation of functional nanometer-sized microgels. The key is to employ a macroinitiator (PEG-acetal-Cl) that carries an acetal linkage between a poly(ethylene glycol) arm chain and a chloride initiating site. From this, star polymers were synthesized via the linking reaction with a divinyl monomer and a ruthenium catalyst in living radical polymerization. The arms were subsequently cleaved by acidolysis of the acetal linker to give soluble microgels (cores free from arms). Full characterization revealed that the microgel cores are spherical, nano-sized (<20 nm), and of relatively low density. Amphiphilic, water-soluble, and thermosensitive arm-free microgels can be obtained by additionally employing functional methacrylate upon arm linking.

Apparatus for measuring time‐resolved light scattering profiles from supercritical polymer solutions undergoing phase separation under high pressure

A light scattering instrument was constructed to investigate the phase diagram and the dynamics of phase separation processes for supercritical polymer solutions. The instrument has the following features: (i) the light scattering cell withstands pressure over 34.3 MPa and temperature up to 573 K, (ii) viscous solutions such as a polymer solution can be easily handled, (iii) a rapid incremental or decremental pressure change as small as 0.01 MPa can be precisely controlled, and (iv) the angular distribution of the scattered intensity can be continuously measured over a wide angular range (0°–30°) at 100 scans/s. The phase diagram of polypropylene/trichlorofluoromethane was measured with the instrument. Some preliminary experimental results for the dynamics of the phase separation of the system are also presented.

Slow spinodal decomposition in binary liquid mixtures of polymers. III. Scaling analyses of later‐stage unmixing

Later‐stage unmixing process of a near critical mixture of polybutadiene (PB)/poly(styrene‐ r‐butadiene)(SBR) were examined at real time t and in situ at several temperatures T by time‐resolved light scattering method. The magnitude of scattering vector qm(t,T) at which the intensity becomes maximum and the maximum intensity Im(t,T) were analyzed in order to characterize the coarsening processes of the later‐stage spinodal decomposition. The variations of Im and qm with t at different T’s were found to fall onto master curves on the reduced plots, thus assuring the scaling postulate that the data obtained at different t and T for given mixtures are properly scaled with the temperature‐dependent characteristic wave number qm(0,T) and characteristic time tc(T).